Integrated circuit package mold assembly

ABSTRACT

An integrated circuit (“IC”) package mold includes an upper mold platen that defines an upper mold cavity for receiving an upper substrate having a die attach side with a plurality of dies mounted thereon and a non-attach side with no dies mounted thereon. The die attach side of the upper substrate faces upwardly. A lower mold platen defines a lower mold cavity for receiving a lower substrate having a die attach side with a plurality dies mounted thereon and a non-attach side with no dies mounted thereon. The die attach side of the lower substrate faces downwardly.

BACKGROUND

Integrated circuits, also referred to as “IC's” or “semiconductor chips”or simply “chips,” are electronic circuits made by diffusion of traceelements into the surface of thin substrates of semiconductor material.Integrated circuits were first produced in the mid 20^(th) Century.Because of their small size and relatively low production cost,integrated circuits are now used in most modern electronics.Semiconductor chips are typically mass produced in the form of a singlewafer that contains a large number of identical integrated circuits. Thewafer is cut (“singulated”) into a number of individual semiconductorchips referred to as “dies” or “dice.”

Dies and sometimes other components such as passive devices are“packaged” to prevent damage to the dies and to facilitate attachment ofthe dies to circuit boards. Various packaging materials and processeshave been used to package integrated circuit dies. One conventionalpackaging method involves mounting individual dies in a predeterminedpattern on a substrate strip. The dies mounted on the substrate stripare then encapsulated in a plastic material, such as by a transfermolding process. Next, the encapsulated dies are singulated intoindividual integrated circuit packages by cutting the encapsulateddie/substrate strip in accordance with the predetermined die mountingpattern. Typical cutting tools include saws and punches. Each integratedcircuit package generally includes at least one die and the underlyingportion of the substrate strip on which it was mounted. The underlyingsubstrate strip is sometimes a leadframe to which the die iselectrically connected.

SUMMARY

An integrated circuit (“IC”) package mold assembly includes an uppermold platen defines an upper mold cavity for receiving an uppersubstrate having a die attach side with a plurality of dies mountedthereon and a non-attach side with no dies mounted thereon. The dieattach side faces upwardly. A lower mold platen defines a lower moldcavity for receiving a lower substrate having a die attach side with aplurality dies mounted thereon and a non-attach side with no diesmounted thereon. The die attach side of the lower substrate facesdownwardly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional elevation view of a prior art mold assembly.

FIG. 2 is a cross-sectional elevation view of an example embodiment of amold assembly that includes a mold with a double cavity configuration.

FIG. 3 is a cross-sectional elevation view of another example embodimentof a double cavity mold assembly.

FIG. 4 is a detail isometric view of a portion of the double cavity moldassembly of FIG. 3.

FIG. 5 is a cross-sectional elevation view of a portion of anotherexample embodiment of a double cavity mold assembly.

FIG. 6 is a flow chart that illustrates a method of making integratedcircuit (“IC”) packages.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional elevation view of a prior art mold assembly10. The mold assembly 10 includes a mold 11, such as an injection mold,that has an upper mold platen 12 and a lower mold platen 14. The uppermold platen 12 has a mold cavity 16 therein in fluid communication witha mold runner 18. The mold assembly 10 also includes a leadframe sheet22 that is positioned within the mold cavity 16. The mold assembly 10further includes a plurality of integrated circuit (IC) dies 24, 26, 28,etc., which are attached to different portions 25, 27, 29, etc., of theleadframe sheet 22. Each of these portions 25, 27, 29 is associated witha separate IC package that will ultimately be formed by singulating(“dicing”) the leadframe sheet 22.

Each of the dies 24, 26, 28 is electrically connected to an associatedleadframe portion 25, 27, 29 of the leadframe sheet 22. In the assembly10 of FIG. 2 the dies are electrically connected to the leadframe sheet22 by bond wires 30. Each bond wire 30 has a first end 32 attached to anassociated die, e.g., die 24, and a second end 34 attached to theleadframe portion, e.g., portion 25, on which the die is mounted.

After insertion of the leadframe sheet 22 and attached wire bonded dies24, etc., the mold 10 is closed and the mold cavity 16 is filled withmolten mold compound 40. The mold compound 40 flows under pressure intothe cavity 16 through the runner 18, which is conventionally connectedto a pressurized source of molten mold compound 40. After the moldcompound 40 has filled the cavity, curing of the mold compoundcommences, initially while the mold 10 is closed, and subsequently afterit is has been opened and the entire assembly of leadframe sheet 22,dies 24, etc. and mold compound 40 has been removed. After removal fromthe mold 10, the portion of the mold compound 40 that was in the runner18 is removed from the portion of the mold compound covering theleadframe sheet 22. The portion of the mold compound that was in therunner is scrapped as waste. This waste is typically around 40% of thetotal amount of mold compound injected in a molding operation.

After the molded leadframe assembly has completed curing it issingulated along saw streets 36, 38, etc., indicated by dashed lines inFIG. 1, into separate IC package units.

FIG. 2 is a cross-sectional elevation view of an example embodiment of amold assembly 110 that includes a mold 111 with a double cavityconfiguration. The mold 111 includes upper and lower mold platens 112,114 having upper and lower mold cavities 116, 118, respectively. Asingle mold runner 120 is in fluid communication with both mold cavities116, 118.

The mold assembly 110 includes an upper substrate 122, which may be aleadframe sheet substrate. Hereafter “leadframe sheet substrate” isreferred to by the shorter phrase “leadframe sheet.” It is to beunderstood that substrates other than leadframe sheets may be used inthe embodiments described in FIGS. 2, 3 and 5.

The substrate 122 has a first end 124 and a second end 126 and has a dieattach side 128 and an opposite or “non-attach side” 129. A lowersubstrate 132, which in this embodiment may be a leadframe sheet, has afirst end 134 and a second end 136 and also includes a die attach side138 and an opposite or non-attach side 139. The upper substrate 122 andthe lower substrate 132 each comprise a plurality of correspondingseparate substrate portions 140 and 142, respectively, which arevertically aligned.

The mold assembly 110 also includes upper and lower substrate dies. Theupper substrate dies 152 are mounted on the upper substrate portions 140of the upper substrate 124 and are electrically connected thereto, as byupper bond wires 154. Similarly lower substrate dies 162 are attached tothe separate substrate portions 142 of the lower substrate 134 and areconnected thereto by lower leadframe bond wires 164. As illustrated inFIG. 2, a liner 170 may be used in some embodiments to separate theupper and lower substrates. In some embodiments when the respectivesubstrates are, for example, nFBGA (New Fine Pitch Ball Grid Arraypackages) substrates or uBGA (Ultra FineLine Ball-Grid Array packages)substrates, rather than leadframe sheets, no liner is needed. The liner170 engages the non-attach sides 129, 139 of the substrates 122, 132.

As further illustrated by FIG. 2, the mold assembly also includes heatedmold compound 178 that is injected into the single mold runner and flowstherethrough to fill both the upper and lower mold cavities 116, 118.The mold compound 178 is initially allowed to cure within the moldcavities 116, 118. Subsequently, the entire substrate/die/bond wire/moldcompound assembly, including the mold compound 178 within the runner120, is removed from the mold 111. The solidified mold compound 178within the runner 120 is then removed and scrapped. Because there is asingle runner 120 associated with both mold cavities 116, 118, the scrapproduced by this new process is substantially reduced as compared to thescrap produced in the conventional process illustrated in FIG. 1.

Next the upper and lower molded substrates 122, etc., 132, etc., areseparated and the liner 170, if used, is removed. Each substrate 122,etc., 132, and associated dies and mold compound, etc., is thensingulated by conventional methods to provide a plurality of separate ICpackages.

FIG. 3 is a cross-sectional elevation view of another example embodimentof a double-sided mold assembly 210 including a mold 211 that has upperand lower mold platens 212, 214 having upper and lower mold cavities216, 218, respectively. The mold 211 has a single runner 220. Theassembly 210 illustrated in FIG. 3 is similar to that illustrated inFIG. 2, and similar structures therein are given the identical referencenumerals as in FIG. 2, except that the reference numerals are 200 seriesrather than 100 series. The structures include: runner 220, uppersubstrate 222 having a first and second ends 224, 226 and die attachside 228 and non-attach side 229 and upper leadframe portions 240; alower substrate 232 with a first and second ends 234, 236 and with a dieattach side 238 and non-attach side 139 and separate upper and lowersubstrate portions 240 and 242; upper dies 252, which may beelectrically connected to the upper substrate by bond wires 254; lowerdies with bond wires 264; liner 270; and mold compound 278. Onedifference in the assembly of FIG. 3 is that upper and lower passivecomponents 253, 255 (e.g., resistors, capacitors and/or inductors) arealso operably mounted on each substrate portion 240 or 242 andelectrically connected to the die(s) on the associated portion 240 or242. Another difference in the assembly of FIG. 3 from that of FIG. 2 isthat holes 280 have been bored through the two substrates 222, 232 andliner sheet 270 after initially sandwiching the liner sheet 270 betweenthe two substrates 222, 232 and before insertion of this substrate/linerassembly into the mold 210. These holes 280 may be bored at each cornerintersection of the substrates when they comprise leadframe sheets 222,232. Four separate leadframe portions are integrally connected. (Theillustrated embodiment shows the holes located at corner intersectionsof the sheets 222, 232, but the holes 280 may be provided at otherlocations. For example, if the binding feature is larger than cornerspace allows, several of the dies may be eliminated and the holes can belocated on the leadframes, or other substrates, where the dies have beeneliminated.)

FIG. 4 is a detail isometric view illustrating a portion of structurelocated around the holes 280 shown in FIG. 3. This structure includes arectangular frame structure 284. The rectangular frame structurelaterally connects first, second, third and fourth upper leadframeportions 286, 288, 290, 292, respectively, of the upper leadframe sheet222. The lower leadframe sheet 232 has an identical configuration (notshown) lying directly below that of sheet 222. The hole 280 passesthrough the center of this rectangular frame portion 284 and an alignedportion 282 of the liner 270.

With reference to FIG. 3, the holes 280 through the assembled sheets222, 270, 232 provide a path for molten mold compound 278. The moldcompound 278 that flows through the holes 280 forms a connectingstructure that holds the two sheets 222, 232 together and in alignmentduring curing, including the curing phase that takes place after removalof the molded leadframe/die/bond wire structure from the mold 211. Theholes 280 may also help to provide pressure equalization between theupper and lower mold cavities 216 and 218 as molten mold compound flowsinto these cavities. The corner frame structure 284 and the moldcompound 278 passing through the holes 280 are bored or cut out andremoved after curing to allow the leadframe sheets 222, 232 to beseparated and subsequently singulated. In another embodiment, the cornerstructure remains intact until singulation and the two connected moldedleadframe sheets 222, 232 and liner 270 are all singulatedsimultaneously with deeper singulation cuts. The upper and lower ICpackage pairs, thus formed, are then separated. In this case,singulation removes the corner structure and connecting mold compoundstructure.

The prior art structure, as shown by FIG. 1, has a metal leadframe sheet22 on one side of the assembly, and epoxy encapsulant compound 40 on theother side. Due to a mismatch in thermal expansion of these twomaterials, when the assembly is ejected from the mold 11 and cools downfrom a high mold temperature, the encapsulated leadframe sheet 22 tendsto warp. Such warping makes the prior art leadframe sheet 22 difficultto work with and, in some cases, is so severe that the molded leadframesheet 22 must be scrapped. In the assembly of FIG. 3, the connectingstructure formed by the mold compound 278 after it solidifies in holes280, combined with the symmetry of the two substrates, prevents warpingof the substrates 222, 232.

FIG. 5 is a cross-sectional elevation view of a portion of anotherexample embodiment of a double-sided mold assembly 310. The moldassembly 310 includes a mold 311 that comprises upper and lower moldplatens 312, 314 having upper and lower mold cavities 316, 318,respectively. The mold 311 may be identical to the mold 211 illustratedin FIG. 3, except that upper projections 317 and lower projections 319extends from the upper and lower mold platens, like symmetricalstalactites and stalagmites, to form a clamping assembly that sandwichesand holds upper and lower leadframes/substrates 322, 332 therebetween.These projections 317, 319 may be provided by ribs that are integrallyformed with the respective upper and lower mold platens 312, 314 or maybe provided by pins inserted through the walls of the mold platens ormay be formed by other means. The projections may engage theleadframes/substrates 322, 332 at the boundaries of adjacent substrateportions, such that any irregularities in the mold compound layer formedby the projections 317, 319 is trimmed off during subsequentsingulation.

This clamping assembly 317, 319 vertically supports the leadframes 322,332, counteracting a tendency of the leadframes to droop under their ownweight prior to the inflow of mold compound (not shown in FIG. 5).

As used herein terms such as up, down, above, under, vertical,horizontal, etc., are used in a relative sense to explain the physicalrelationship between various structures shown in the drawings, ratherthan in an absolute sense indicating an orientation of objects within agravitational field.

FIG. 6 is a flow chart that illustrates a method of making integratedcircuit (“IC”) packages. The method includes, as shown at 601, placingfirst and second IC package substrates having a plurality of individualportions associated with individual IC packages in non-attach sidefacing, mirror image relationship. The method also includes, as shown at602, placing the first and second substrates in a mold having upper andlower cavities with the first substrate positioned in an upper moldplaten cavity and the second substrate positioned in a lower mold platencavity that is in fluid communication with the upper mold platen cavity.As shown at 603, the method further includes filling the upper and lowermold cavities with molten mold compound.

Certain specific embodiments of double cavity mold assemblies andmethods of use thereof have been expressly described in detail herein toaid those reading this disclosure to understand the inventive conceptsinvolved. Alternative embodiments of such mold assemblies and methodswill occur to those skilled in the art after reading this disclosure. Itis intended that the language of the appended claims be broadlyconstrued to cover such alternative embodiments, except as limited bythe prior art.

What is claimed is:
 1. An integrated circuit (“IC”) package moldassembly comprising: an upper mold platen defining an upper mold cavityfor receiving an upper substrate having a die attach side with aplurality of dies mounted thereon and a non-attach side with no diesmounted thereon, wherein said die attach side is facing upwardly; and alower mold platen defining a lower mold cavity for receiving a lowersubstrate having a die attach side with a plurality dies mounted thereonand a non-attach side with no dies mounted thereon, wherein said dieattach side of said lower substrate is facing downwardly.
 2. Theassembly of claim 1 wherein said upper and lower mold platens comprisesat least one pair of aligned projections extending into said moldcavities for engaging said upper and lower substrates therebetween. 3.The assembly of claim 1 further comprising a single runner in fluidcommunication with said upper and lower mold cavities.
 4. An integratedcircuit (“IC”) package mold assembly comprising: an upper mold platendefining an upper mold cavity; a lower mold platen defining a lower moldcavity; an upper substrate positioned in said upper mold cavity andhaving a plurality of integrally connected substrate portions, each saidupper substrate portion having a die attach side and a non-attach side,IC dies being mounted on said die attach sides of said plurality ofupper substrate portions; and a lower substrate positioned in said lowermold cavity and having a plurality of integrally connected lowersubstrate portions, each lower substrate portion having a die attachside and a non-attach side, IC dies being mounted on said die attachsides of said plurality of lower substrate portions; wherein said upperand lower substrates are positioned with said non-attach sides of saidsubstrate portions thereof positioned in facing relationship.
 5. Theassembly of claim 4 wherein said upper and lower substrates compriseupper and lower leadframe substrates and further comprising a linerpositioned between said upper and lower leadframe substrates.
 6. Theassembly of claim 4 wherein said upper and lower substrates comprisesnFBGA (New Fine Pitch Ball Grid Array) substrates.
 7. The assembly ofclaim 4 wherein said upper and lower substrates comprises flex-tapesubstrates.
 8. The assembly of claim 4 wherein said upper and lowersubstrates have aligned holes extending therethrough.
 9. The assembly ofclaim 8 further comprising a liner positioned between said upper andlower substrates and having holes therein aligned with said holes insaid upper and lower substrates.
 10. The assembly of claim 9 whereineach of said upper and lower substrates comprise leadframe sheetsubstrates with leadframe corner connection structures that connectleadframe portions on each corresponding leadframe sheet substrate;wherein said leadframe corner connection structures have openingstherein that are aligned with corresponding ones of said holes extendingthrough said liner.
 11. The assembly of claim 8, said upper and lowermold cavities being filled with mold compound that fills said alignedholes extending through said substrates.
 12. A method of makingintegrated circuit (“IC”) packages comprising: placing first and secondIC package substrates having a plurality of individual portionsassociated with individual IC packages in non-attach side facing, mirrorimage relationship; placing the first and second substrates in a moldhaving upper and lower cavities with the first substrate positioned inan upper mold platen cavity and the second substrate positioned in alower mold platen cavity that is in fluid communication with the uppermold platen cavity; and filling the upper and lower mold cavities withmolten mold compound.
 13. The method of claim 12 further comprisingengaging aligned portions of the first and second IC package substrateswith opposite mold platen projections.
 14. The method of claim 13further comprising producing a plurality of holes extending throughaligned portions of the first and second substrates.
 15. The method ofclaim 14 further comprising flowing mold compound into the mold to moldthe two substrates including flowing mold compound through the pluralityof holes to form connecting structures to hold the two molded substratestogether.
 16. The method of claim 15 further comprising: curing the moldcompound; and removing connecting structures holding the moldedsubstrates together.
 17. The method of claim 16 further comprisingseparating the molded substrates.
 18. The method of claim 17 furthercomprising dicing the separated molded substrates.
 19. The method ofclaim 15 further comprising dicing the connected molded substrates. 20.The method of claim 19 further comprising removing the connectingstructure during said dicing.